1. Field of the Invention
This invention relates to an electronic flash apparatus for a camera, and more particularly to an indicating device of the electronic flash apparatus for use in flash photography.
2. Description of the Prior Art
In a recently introduced electronic flash apparatus, flash light reflected from an object being photographed is detected and when the light has reached a predetermined level, the flash is stopped. This type of device is hereinafter referred to as a "computer type electronic flash apparatus." Of course, such computer type electronic flash apparatus includes ones capable of selecting a desired diaphragm value.
With flash apparatus, it is impossible to produce proper exposures for very distant objects. Accordingly, the object distance is limited to a particular range for which proper exposure can be made. In addition thereto, this particular range (hereinafter referred to as "proper distance range") varies with at least one exposure control parameter or aperture size. For example, assuming that the flash output of the flash apparatus is GN=16, when an aperture size of F=4 is selected, the corresponding proper distance range becomes 4 (meters), and at F=2, it becomes 8 (meters).
Therefore, even in the case of the latter (diaphragm value selectable) computer type electronic flash apparatus, the proper distance range varies in accordance with the set diaphragm value.
By the way, this proper distance range can be easily calculated from the light amount of the flash apparatus and the set diaphragm value. However, it is very troublesome for the latter computer type flash apparatus to calculate the proper distance range each time the set diaphragm value is changed.
On this account, a solution has been proposed in which an instruction plate having described thereon a list of proper distance ranges corresponding to the respective set diaphragm values is provided as mounted on the back of the computer type electronic flash apparatus (the term "back" means the surface of the electronic flash apparatus which faces the photographer).
This third computer type electronic flash apparatus has a preset member for presetting an aperture size positioned on the front surface thereof. Thus, it is first necessary for the photographer to change the angular position of the flash apparatus to read out the preset diaphragm value of the preset member provided on the front surface of the flash apparatus. Thereafter, the operator must again change the angular position of the flash apparatus to look at the instruction plate for the proper distance observation as the instruction plate is mounted on the back surface of the flash apparatus. Otherwise, it is impossible to recognize whether or not the object falls in the proper distance range. This constitutes a very troublesome problem.